1. Field of the Invention
The present invention relates to a self-aligned manufacturing method of a thin film transistor, especially to a self-aligned manufacturing method of a thin film transistor for forming a single-crystal bottom-gate and an offset drain.
2. Description of the Prior Art
Since in the single-crystal bottom gate the single-crystal is used as a gate, the gate insulation layer of gate can be grown directly on a single-crystal silicon, thus the quality thereof is better than those grown a polysilicon. Therefore, inherently the single-crystal bottom-gate has a particular advantage of forming high quality gate insulation layer. In 1990, Pfiester and other researchers has disclosed a self-aligning method for TFT with single-crystal gate [3], as shown in FIG. 1. However, this method is confined to fabricate a conventional non-offset drain transistor.
In recent years, it has been reported in many papers that the leakage current of a thin film transistor may be reduced effectively so to derive a preferred on/off current ratio in order to assert to obtain a high quality thin film transistor. For example, in reference [1, 2], if the length of an offset gate is within the range of 0.3-0.4 micrometers, the leakage current may be reduced effectively within the range of ten times to several hundred times, while the driving current is decreased slightly, therefore, the on/off current ratio is greatly improved. Thus a thin film transistor for forming a single-crystal bottom-gate and an offset drain will be an ideal element structure in the future. But nowadays there are no reports about a self-aligned forming method of a thin film transistor for forming a single-crystal bottom-gate and an offset drain.